1. Field of the Invention
This invention generally relates to the field of line threading devices for elongated conduits and, in particular, to an apparatus and method of installing utility lines, such as telephone, fiber optic, or electrical wiring in a conduit.
2. Background of the Prior Art
As most electricians are aware, one of the most difficult chores that they encounter is the threading of wires and cable through elongated tubular conduits. Depending on the gauge and composition of the wires, as well as the length of the conduits and the number and sharpness of the bends in the conduit, feed of the wires through the conduits can be a difficult and trying chore. These difficulties have spurred much activity in terms of time and effort in an attempt to devise a suitable system or apparatus for “fishing” conduit that would be effective, inexpensive, and simple enough to be conducted by unskilled labor working under the direction of a professional electrician.
One approach has involved the use of a “fish tape” which consists of a thin, highly flexible metal strap or tape that can be inserted into one end of the conduit and pushed through and out the other end of the conduit. The wire is then connected to the fish tape at one end of the conduit and the fish tape drawn back through the conduit with the wire attached. Such a system works fairly well, where the length of conduit is short, and the bends in the conduit are kept shallow and few in number. However, this is not always practicable.
Another approach in common use involves introducing a light weight rope, cord, or thread into the conduit by attaching it to a projectile or missile that is then inserted into one end of the conduit and driven through by air or other fluid admitted under pressure into the conduit behind the projectile. Alternatively, a partial vacuum can be created in the conduit ahead of the projectile, causing the projectile to be sucked through the conduit. In each instance, the cord is drawn with the projectile or missile through the conduit, the cord then being useful as a pull line to introduce the wire.
Such projectiles or missiles have taken several forms. For example, it was early proposed that the missile be light in weight and fit loosely within the conduit so that it would not catch as it is driven through the conduit. Such a projectile was usually given the shape of a cone, a cup, or a thimble and arranged so as to present a flared wide area surface to increase its response to the force of the pressurized fluid. However, as the projectile moved away from the source of pressurized air, the inefficiency of the system became more pronounced, and the missile would decelerate and often come to a halt short of the conduit end. The employment of such a loosely fitting missile was particularly unsatisfactory where it was proposed to move the projectile in response to creation of a vacuum in the conduit ahead of the missile.
Although each of the projectiles worked satisfactorily under controlled circumstances, each presented its own special problems. In many instances, the conduit may be in the ceiling requiring the high pressure or vacuum hose to be lifted over the operator's head throughout the duration of the procedure. Often, the project would get stuck in the conduit. Particularly in the case of very long conduits, the pressure or vacuum system tends to be less effective.
Accordingly, there remains a need for a safe and simple apparatus that is effective in threading a line into a conduit to install telephone, electric, or fiber optic lines.